The primary steps in the utilization of certain carbohydrates by oral streptococci are being characterized biochemically and physiologically. Such information should provide insight into the etiology of carious lesions of the teeth, ecological interactions in the oral environment and the evolution of specifically adapted oral microbes. Current research is directed at biochemical characterization, purification and comparative studies on four enzymes involved in sucrose dissimilation; extracellular invertase, intracellular invertase, glucokinase and fructokinase. Further experiments are directed at determining the factors which regulate the synthesis of these enzymes at the DNA transcription level and the modulation of their activity by growth sources and other metabolites. It appears that several distinct patterns of regulation exist amongst various oral streptococci.